System
You can increase hero stars by using shards, increasing hero stars will increase base stats (hp/def) and unlock some passive.
For example, Ame is a 3* base star, so her burst 2 is already unlocked, she will unlock 3% ally crit chance and weakness gauge damage +1 at 4*, burst 3 at 5* and another 3% crit chance at 6* + 25 action points at battle start.
Shard cost
| Base Unit Rarity | 2 star | 3 star | 4 star | 5 star | 6 star | Total |
|---|---|---|---|---|---|---|
 | 30 | 40 | 50 | 70 | 100 | 290 |
| 0 | 65 | 85 | 100 | 200 | 450 |
| 0 | 0 | 150 | 300 | 450 | 900 |
Where to get shards
| Source | Number |
|---|---|
| Recruit | 10 per hero dupe if 1* and 2* 50 per hero 3* dupe 150 if the 3* is rated-up (rate-up banner or premium demiurge) |
| Friendship shop | 1/2* ticket per week |
| Event shop | Usually 50 shard to farm on featured heroes per event |
| Pieces | You can trade 10 green shard for 1 hero shard, you get green shard in gacha pulls |
| Side story | Unlocked when you pull 1 copy of a hero 10 attemps per day, 5 max for the same unit. 15 shards per 3*, for a total of 30 per day 10 shard per 2* or 1* seconday unit for a total of 20 per day. Secondary units are selected in rewards menu before starting the fight, the selection depends of the element of the unit, a water main 3* story will allow you to pick any water 1* and 2* |
Best strategy to follow
First objective:
The best route to follow is to get all your units to 4 star rather than trying to 6* only one or 2 units.
4 star is the best value low effort you want for your units, that means you can 4* 2 units per 10 days, the main reason here is to get thet weakness gauge damage bonus, this is a priority for your progression as most of the boss will ask you to get a chain break and sometime in early you only miss 1 or 2 wgd damage missing.
So you will want to focus on your main 3* to 4*, and as secondary, the 2* you plan to use in content (Dolly/Tio/Marian for example…) so they can be relevant.
Second objective:
Units with a burst 3 you really want to unlock, like Mene for her extra heal or tamara for her extra turn.
Third objective:
If all your previous objective are done you can start the very long journey to 6*, it will take you 60 days to max one unit, but sometime they worth it, for example Mene 6* is a +10 bonus speed total for your team.